Exam qs Flashcards
Similarities and differences of tRNA and mRNA?
mRNA doesn’t have hydrogen bonds, tRNA does
mRNA doesn’t have an amino acid binding site, tRNA does
mRNA has more nucleotides
différent mRNAs have different lengths, tRNAs have similar lengths
How translation leads to the production of a polypeptide (starting with mRNA in the cytoplasm)
mRNA binds to ribosome,
Ribosome moves to the start codon,
tRNA brings an amino acid,
anticodon on tRNA is complimentary to the codon on mRNA,
Ribosome moves along to the next codon,
Amino acids are joined by peptide bonds (undergo condensation reaction)
What is the proteome of a cell?
All the different proteins produced by a cell.
Describe the role of a ribosome in the production of a polypeptide?
mRNA binds to the ribosome,
Idea of 2 codons,
allows the tRNA with anti codons to bind,
Catalyses the formation of peptide bonds between amino acids
Ribosome moves along mRNA to the next codon
In a eukaryotic cell, the base sequence of the mRNA might be different from the sequence of pre-mRNA, why?
mRNA hasn’t been spliced yet so still contains introns and exons.
Explain how the organic bases help to stabilise the structure of DNA?
Many hydrogen bonds provide a lot of strength
The hydrogen bonds between the base pairs hold together the two strands of DNA
Two proteins have the same number and type of amino acids but different tertiary structures, why?
The sequence of amino acids is different so the primary structure is different.
This means that disulfide bonds form in different places.
Describe the structure of proteins?
- Polymer of amino acids
- amino acids joined by peptide bonds which are
- formed by condensation reactions
- primary structure is the order of amino acids
- secondary structure is the folding of the polypeptide chain due to hydrogen bonds
- tertiary structure is the secondary structure further folding to form a 3D structure due to hydrogen and ionic and disulfide bonds
- quaternary structure is multiple polypeptide chains
Explain how formation of an ES complex increases the rate of reaction?
When an ES complex forms the active site changes shape as it moulds around the substrate, this puts pressure on the substrate causing its hydrogen and ionic bonds to become distorted (weakening them) so less energy is required to break them, and activation energy is reduced.
When x (in this case, ATR ) phosphorylates other enzymes, these enzymes become able to bind to their substrates. Why?
Because ATR changes the shape of the enzyme’s tertiary structure which changes the shape of the active site so that it becomes complimentary to the substrate.
Suggest how the acidic conditions created by osteoclasts cause the inactive form of the protein osteocalcin to change into the active form of osteocalcin?
The change in pH breaks the hydrogen and ionic bonds which changes the tertiary structure. (Then the tertiary structure becomes complimentary to the substrate so osteocalcin becomes active)
[graph showing the enzyme activity in washing powder over time at 50 degrees (less steep negative gradient going down) compared to 60 degrees (really steep negative gradient going down)]
- both denatured
- denaturation at 60 degrees is faster because there’s more kinetic energy
- at the high temperatures the ionic and hydrogen bonds are broken
- this causes the tertiary structure to change shape so that it’s no longer complimentary with the substrate
Experiment adding different concentrations of lipase to lipids to see how the concentration affects the lipids hydrolysis…. what is the control?
Boiled lipase solution
ADP + Pi goes to ?
ATP + H2O
An antibiotic inhibits bacterial ATP synthase enzyme but not human ATP synthase enzyme, why?
Human ATP synthase has a different active site to bacterial ATP synthase (so the antibiotic isn’t complimentary to the active site of the human ATP synthase which means they don’t bind and the reaction ISN’t stopped)
Give two ways ATP is a suitable energy source in cells?
- releases small amounts of energy
- it can be synthesised quickly (because it only takes a single reaction for it to be broken down)
Which biological processes involve electron transport chains?
Photosynthesis
Aerobic respiration
In which biological processes is ATP produced?
Photosynthesis
Anaerobic respiration
Aerobic respiration
Which biological processes occur in organelles?
Photosynthesis
Aerobic respiration
Gland cells produce and secrete breast milk which contains a high concentration of protein.Explain why there are many mitochondria and Golgi vesicles in gland cells.
Many mitochondria mean lots of ATP is produced for active transport.
Many Golgi vesicles to transport the milk proteins out of the cell
How is the Golgi body involved in absorption of lipids?
- modifies triglycerides
- combines triglycerides with proteins
- packages them for exocytosis
Which organelles have a double outer membrane?
Mitochondria and chloroplast
What is a structure that isn’t present in animal cells that is. Present in plant cells?
A permanent vacuole
Explain why the same organelles may appear to be different shapes in a biological drawing?
Thin sections
cut at different angles
Through different planes
Explain why the student only used the first 5mm of the onion root tip?
It’s where mitosis occurs the most
Explain why a student presses down firmly on the coverslip?
To spread the tissues so they are one cell thick and easier to observe
Why might you need to dilute a solution?
To make it easier to see cells
Explain how the stain allowed the doctor to see the WBC’s amongst the RBCs?
Because the dye stained the nucleus of the white blood cells and red blood cells don’t have a nucleus so anything stained must be a white blood cell.
Explain how the detergent which dissolves lipids helps to release proteins from a cell?
It dissolves the phospholipid bilayer of the membrane which breaks open because it is made of phospholipids
Comparisons of TEM and Optical Microscope?
OM-beam of light
TEM-beam of electrons
OM- doesn’t have to be thin
TEM- specimen must be thin
OM- focuses using lenses
TEM-focuses using magnets
OM-shows colour
TEM- no colour
OM- specimen can be alive
TEM-specimen must be dead
Explain why the solution the biologist used was ice cold, buffered and the same water potential as the liver tissue?
Ice cold - to reduce enzyme activity and prevent the digestion of organelles
Buffered - maintain constant pH so enzymes don’t denature
Same water potential - prevent cells shrinking or expanding as a result of water moving in or out
Explain how a mutation could lead to a faulty protein?
The gene that codes for the protein may have a mutation which means that there is a change in the sequence of amino acids.
This results in a different primary structure which then affects the tertiary structure.
Why did blood clot when a boy with faulty IX’s blood was mixed with blood from someone with a faulty VIII?
Because IX had a complimentary active site to VIII so the pathway can continue and blood can clot
Explain why a mutation involving deletion of a base may have a greater effect than one involving substitution of one base for another?
Deletion of a base causes a frame shift which means that the bases are not read in the correct groups of three (and the entire sequence of amino acids would be affected) whereas substitution only one triplet would be affected and there is also a chance that it will still code for the same amino acid due to DNA be degenerative. - substitution might result in a silent mutation.
Describe how a deletion mutation alters the gene?
Deletion is the removal of one or more bases. It means there is a loss of a nucleotide which will cause a frame shift.
Name a mutagenic agent?
Alpha radiation
Explain how mutation 2 could lead to the formation of a non-functional enzyme?
It has a different triplet of bases (CTG which codes for Leu instead of Val). This results in a different sequence of amino acids so a different structure. Therefore hydrogen and ionic bonds form in different places to create a different tertiary structure which may not be complimentary to the substrate, stopping the enzyme from working. ES complexes cannot be formed.
During which part of the cell are gene mutations likely to occur?
S phase because that is when DNA is replicated
Explain how the chromosome number is halved during meiosis?
One from each of the homologous pair of chromosomes goes to each opposite pole
Describe the process of crossing over and explain how it increases genetic diversity?
Homologous pairs of chromosomes associate
Chiasmata form
Lengths of non sister chromatids are exchanged
Producing new combinations of alleles
Describe how a change in the chromosome number was produced?
In meiosis
The sister chromatids did not separate
Explain why all cells in the body will have this mutation?
The mutation forms the gamete which makes a zygote and all cells are derived from that zygote in mitosis
Explain the role of independent segregation in meiosis?
Provide genetic variation
Allows different combinations of maternal and paternal chromosomes
To produce haploid cells
Allows homologous pairs to arrange randomly at the equator of the cell and separate
Describe and explain the process that occur during meiosis which increase genetic variation.
Crossing over leads to the exchange of parts of alleles between homologous chromosomes and both chromosomes create a new combination of alleles
Homologous chromosomes pair up, independent segregation, maternal and paternal chromosomes are reshuffled in any combination.
Describe and explain the appearance of one of the chromosomes in cell X.
Chromosomes are formed of 2 chromatids
Because DNA replication occurred
The sister chromatids are held together by centromeres
Identify one even that occurred during division 2 but not division 1
No separation of chromatids
Describe what has happened during division 1
Chromosomes are in a homologous pair
One of each goes to each daughter cell
Suggest why the cell membrane appeared as two dark lines when dye was added?
Phospholipid bilayer
Hydrophilic phosphate heads on inside and outside
So stain binds to inside and outside producing two dark lines
Why is Y unsaturated?
It contains a carbon-carbon double bond
Suggest why red blood cells have more cholesterol in their cell membranes?
They float around freely so it provides more support. In comparison other cells may be bound to something else which provides support.
Describe the difference between the structure of a triglyceride molecule and the structure of a phospholipid molecule?
The third fatty acid tail in the phospholipid is replaced by a phosphate group.
